Bipolar transistor with improved stability

ABSTRACT

Instability and drift sometimes observed in bipolar transistors, having a portion of the base extending to the transistor surface between the emitter and base contact, can be reduced or eliminated by providing a further doped region of the same conductivity type as the emitter at the transistor surface between the emitter and the base contact. The further region is desirably more heavily doped than the base region at the surface and less heavily doped than the adjacent emitter. In another embodiment, a still or yet further region of the same conductivity type as the emitter is provided either between the further region and the emitter or laterally within the emitter. The still or yet further region is desirably more heavily doped than the further region. Such further regions shield the near surface base region from trapped charge that may be present in dielectric layers or interfaces overlying the transistor surface.

FIELD OF THE INVENTION

The present invention generally relates to semiconductor devices andcircuits and methods for fabricating semiconductor devices and circuits,and more particularly relates to semiconductor devices and circuitsembodying contiguous NPN or PNP regions, as for example, bipolartransistors.

BACKGROUND OF THE INVENTION

Contiguous NPN or PNP regions and bipolar transistors are much used inmodern electronics as individual devices and as part of variousintegrated circuits (ICs). The stability of such devices as a functionof time and/or usage is an important property. It has been found undersome circumstances, that the base current, the collector current, thecurrent gain and/or other properties of such devices may drift as afunction of time and/or usage. This is undesirable. Accordingly, a needcontinues to exist for improved bipolar transistors and other contiguousNPN or PNP regions, and methods for manufacturing the same, in whichsuch drift in properties is reduced or eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 shows a simplified cross-sectional view of an improved bipolartransistor according to an embodiment of the present invention;

FIG. 2 shows a simplified cross-sectional view of an improved bipolartransistor according to another embodiment of the present invention;

FIG. 3 shows a simplified cross-sectional view of an improved bipolartransistor according to still another embodiment of the presentinvention;

FIG. 4 is a simplified flow chart of a method of manufacture accordingto a further embodiment of the present invention; and

FIGS. 5-12 show simplified cross-sectional views of the bipolartransistors of FIGS. 1-3 during various stages of manufacture.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, or the following detailed description.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the invention. Additionally, elements in thedrawing figures are not necessarily drawn to scale. For example, thedimensions of some of the elements or regions in the figures may beexaggerated relative to other elements or regions to help improveunderstanding of embodiments of the invention.

The terms “first,” “second,” “third,” “fourth” and the like in thedescription and the claims, if any, may be used for distinguishingbetween similar elements or steps and not necessarily for describing aparticular sequential or chronological order. It is to be understoodthat the terms so used are interchangeable under appropriatecircumstances such that the embodiments of the invention describedherein are, for example, capable of operation or arrangement insequences other than those illustrated or otherwise described herein.Furthermore, the terms “comprise,” “include,” “have” and any variationsthereof, are intended to cover non-exclusive inclusions, such that aprocess, method, article, or apparatus that comprises a list of elementsor steps is not necessarily limited to those elements, but may includeother elements or steps not expressly listed or inherent to suchprocess, method, article, or apparatus. The term “coupled,” as usedherein, is defined as directly or indirectly connected in an electricalor non-electrical manner. As used herein the terms “substantial” and“substantially” mean sufficient to accomplish the stated purpose in apractical manner and that minor imperfections, if any, are notsignificant for the stated purpose.

As used herein, the term “semiconductor” and the abbreviation “SC” areintended to include any semiconductor whether single crystal,poly-crystalline or amorphous and to include type IV semiconductors,non-type IV semiconductors, compound semiconductors as well as organicand inorganic semiconductors. Further, the terms “substrate” and“semiconductor substrate” and “SC substrate” are intended to includesingle crystal structures, polycrystalline structures, amorphousstructures, thin film structures, layered structures as for example andnot intended to be limiting, semiconductor-on-insulator (SOI)structures, and combinations thereof.

For convenience of explanation and not intended to be limiting,semiconductor devices and methods of fabrication are described hereinfor silicon semiconductors, but persons of skill in the art willunderstand that other semiconductor materials may also be used.Additionally, various device types and/or doped SC regions may beidentified as being of N type or P type, but this is merely forconvenience of description and not intended to be limiting, and suchidentification may be replaced by the more general description of beingof a “first conductivity type” or a “second, opposite conductivity type”where the first type may be either N or P type and the second type isthen either P or N type. As used herein, the term “bipolar transistor”,singular or plural, is intended to include any type of semiconductordevice employing contiguous NPN or PNP regions some of which exhibitminority carrier conduction, even though further doped regions may beincluded in such devices. Various embodiments of the invention will beillustrated for NPN bipolar transistors, but this is merely forconvenience of description and is not intended to be limiting. Personsof skill in the art will understand that PNP transistors and othersemiconductor devices and circuits embodying either or both NPN and PNPcombinations may be provided by appropriate interchange of conductivitytypes in the various regions.

It has been discovered that bipolar transistor instabilities orproperties drift can arise from surface effects in the base between theemitter and the base contact region. Such surface effects may arise fromcharge trapped in overlying dielectric layers or at interfaces betweenoverlying dielectric and conductor layers or from other causes. Chargetrapped in such overlying layers can affect the carrier concentration inbase region(s) at or near the SC surface, thereby altering theproperties of the base and its effect on the collector current. Thistrapped charge and therefore the near-surface carrier concentration canchange with time and/or usage. This is believed to give rise to theobserved drift in transistor properties. It has been discovered that thesusceptibility of such transistors or other devices to these effects canbe reduced or eliminated by modifying the doping of the near-surfaceregions of the base between the base contact region(s) and the emitter,as illustrated in connection with FIGS. 1-3 and elsewhere herein.

FIG. 1 shows simplified cross-sectional view 20 of improved bipolartransistor 21 according to an embodiment of the present invention.Transistor 21 comprises substrate 22 (e.g., P type SC) having lowersurface 23 and in or on which have been formed (e.g., N type) buriedlayer (BL) 24, base regions 26, 28 (e.g., P type), and (e.g., N+)emitter 30 proximate upper surface 31. For convenience of descriptionand not intended to be limiting, the region between rear or lowersurface 23 and front or upper surface 31 is referred to as semiconductor(SC) 33, even though in some embodiments it may comprise non-SCelements, as for example and not intended to be limiting in the case ofa semiconductor-on-insulator (SOI) structure. Base contacts (e.g., P+)32 extend from surface 31 into portion 28 of (e.g., P type) base 26, 28and are laterally separated from emitter 30 by distance 54. Collectorcontacts (e.g., N+) 34 proximate surface 31 are in ohmic contact withdeep (e.g., N type) wells 35 that extend to buried layer (BL) 24,thereby providing front surface access to BL 24 that acts as the primarycollector of transistor 21. For convenience of description and notintended to be limiting, such wells may be identified by theabbreviation “NW” or “NWs” or WELLs even though it will be understoodthat in various embodiments they may have either N or P conductivitytype. In still other embodiments, deep WELLs 35 may be omitted andcollector contact made via substrate 22 of appropriate conductivity andrear surface 23. Either arrangement is useful.

Extending from surface 31 into SC 33 are shallow trench isolation (STI)regions 36 having portions 361, 362 separating WELLs 35 from, forexample, base portion 28 at surface 31 and WELLs 35 from other portionsof SC 33 lying laterally outboard of transistor 21. While two basecontacts 32, two collector contacts 34, two STI regions 361 and two STIregions 362 are shown in FIGS. 1-3 and elsewhere, it will be understoodby those of skill in the art that such regions may be coupled, e.g., inthe case of regions 32, 34 by conductive leads overlying surface 31, ormay be parts of common (e.g., annular) regions 32, 34, 361, 362 that liein front of and/or behind the plane of FIGS. 1-3.

Overlying surface 31 is blocking layer 38 of, for example, an oxide andnitride stack, having portion 381 lying between STI regions 362 and basecontact(s) 32, and portion 382 lying between base contact(s) 32 andemitter 30. Blocking layer 38 is preferred but may be omitted in furtherembodiments. Overlying surface 31 and blocking layer 38 is dielectriclayer 40 in which openings (indicated schematically) are providedextending to emitter 30, base contact(s) 32 and collector contact(s) 34,so that emitter terminal 42, base terminal 43 and collector terminal 44may be provided in a conventional manner.

By way of example and not intended to be limiting: (a) substrate 22 whenof SC material has doping usefully in the range of about 1E14 to 1E17atoms per cm³, more conveniently in the range of about 5E14 to 1E16atoms per cm³, and preferably about 1-5E15 atoms per cm³; (b) BL 24 hasdoping usefully in the range of about 1E16 to 5E19 atoms per cm³, moreconveniently in the range of about 1E17 to 1E19 atoms per cm³, andpreferably about 5E17 to 5E18 atoms per cm³; (c) base region 26 hasdoping usefully in the range of about 1E14 to 1E18 atoms per cm³, moreconveniently in the range of about 5E14 to 5E16 atoms per cm³, andpreferably about 1-5E15 atoms per cm³; (d) base region 28 has dopingusefully in the range of about 1E14 to 1E19 atoms per cm³, moreconveniently in the range of about 1E16 to 1E18 atoms per cm³, andpreferably about 1-5E17 atoms per cm³; (e) emitter 30 has dopingusefully in the range of about 1E19 to 1E23 atoms per cm³, moreconveniently in the range of about 1E20 to 1E22 atoms per cm³, andpreferably about 5E20 to 5E21 atoms per cm³; (f) base contacts 32 havedoping usefully in the range of about 1E19 to 1E23 atoms per cm³, moreconveniently in the range of about 1E20 to 1E22 atoms per cm³, andpreferably about 5E20 to 5E21 atoms per cm³; (g) collector contacts 34have doping usefully in the range of about 1E19 to 1E23 atoms per cm³,more conveniently in the range of about 1E20 to 1E22 atoms per cm³, andpreferably about 5E20 to 5E21 atoms per cm³; and (h) collector wells 35have doping usefully in the range of about 1E16 to 5E19 atoms per cm³,more conveniently in the range of about 1E17 to 1E19 atoms per cm³, andpreferably about 5E17 to 5E18 atoms per cm³. Higher and lower values mayalso be used for these various regions. Stated another way, base region28 has a doping density about 10⁻³ times that of emitter 30 and about10² times that of base region 26, but larger and smaller ratios may alsobe used.

It has been found that the instability and/or drift previously describedcan be minimized by providing relatively shallow (e.g., N type)region(s) 48 in (e.g., P type) base region 28, extending between basecontact(s) 32 and emitter 30 proximate surface 31. Region(s) 48 shouldbe of opposite conductivity type than base region 28 and the sameconductivity type as emitter 30. Where emitter 30 has a peak dopingdensity such as described above, located about 0.1 to 0.3 micrometersbeneath surface 31, then region(s) 48 has a peak doping density usefullyin the range of about 1E16 to 5E19 atoms per cm³, more conveniently inthe range of about 1E17 to 1E19 atoms per cm³, and preferably about0.5-2.0E18 atoms per cm³ near surface 31, dropping off by a factor ofabout 10² by about 0.1 to 0.2 micrometers beneath surface 31. Statedanother way, it is desirable that region 48 be of opposite conductivitytype to base region 28 and with a surface concentration about an orderof magnitude larger than the doping density of base region 28. It isfurther useful that the doping profile of region 48 fall to about equalor less than that of base region 28 within a depth beneath surface 31equal or less than the emitter depth, desirably within about 5 to 60percent of the emitter depth and preferably within about 25 percent ofthe emitter depth, but larger or smaller depths may also be used inother embodiments.

FIG. 2 shows simplified cross-sectional view 50 of improved bipolartransistor 51 according to another embodiment of the present invention.Transistor 51 of FIG. 2 is similar in many respects to transistor 21 ofFIG. 1. Accordingly, the same reference numbers are used to identifysimilar regions and the discussion of such regions (e.g., location,doping, depth, etc.) given in connection with transistor 21 of FIG. 1also applies to the analogous regions in transistor 51 of FIG. 2.Transistor 51 of FIG. 2 differs from transistor 21 of FIG. 1 by theaddition of (e.g., N type) region(s) 52 at the lateral periphery of(e.g., N+) emitter 30 between emitter 30 and (e.g., N type) regions 48at surface 31. Region(s) 52 have peak doping usefully in the range ofabout 1E16 to 1E20 atoms per cm³, more conveniently in the range ofabout 1E17 to 5E19 atoms per cm³, and preferably about 1E18 to 1E19atoms per cm³ and depth somewhat similar to that of emitter 30, buthigher or lower doping and different depths may also be used inadditional embodiments. Stated another way, it is useful that regions 52have a doping density that is in the range of about 1 to 100, moreconveniently about 1.5 to 20 and preferably about 2 to 10 times that offurther regions 48. Lateral width 53 of regions 52 is usefully about 0to 90 percent, more conveniently about 10 to 70 percent and preferablyabout 50 percent of spacing 54 between base contact 32 and emitter 30.

FIG. 3 shows simplified cross-sectional view 60 of improved bipolartransistor 61 according to yet another embodiment of the presentinvention. Transistor 61 of FIG. 3 is similar in many respects totransistor 21 of FIG. 1. Accordingly, the same reference numbers areused to identify similar regions and the discussion of such regions(e.g., location, doping, depth, etc.) given in connection withtransistor 21 of FIG. 1 also applies generally to the analogous regionsin transistor 61 of FIG. 3. Transistor 61 of FIG. 3 differs fromtransistor 21 of FIG. 1 by the addition of (e.g., N type) region 62 ofwidth 63, preferably within the lateral periphery of (e.g., N+) emitter30 of width 65, proximate surface 31. Region 62 has peak doping usefullyin the range of about 1E16 to 1E20 atoms per cm³, more conveniently inthe range of about 1E17 to 5E19 atoms per cm³, and preferably about 1E18to 1E19 atoms per cm³, but higher or lower doping and different depthsmay also be used in additional embodiments. The combination of dopedregion 62 and emitter 30 results in the portion of the base underlyingregion 62 being slightly counter-doped so that emitter-base junction 64beneath region 62 is slightly deeper than emitter-base junction 66 lyinglaterally outside of region 62. It has been found that this usefullyimproves the beta of transistor 61. Lateral width 63 of region 62 isusefully about 10 to 100 percent, more conveniently about 15 to 100percent and preferably about 90 percent of lateral width 65 of emitter30.

In plan view, transistors 21, 51, 61 may have in some embodiments, anannular plan view shape so that regions 36, 35, 32, 30, 48, 52, 361, 36,381, 382, etc., shown in FIGS. 1-3 are substantially closed in planview. In other embodiments, regions 36, 35, 32, 30, 48, 52, 361, 36,381, 382, etc., may have rectilinear or other non-annular plan viewshapes terminating, for example, in planes above and below the plane ofFIGS. 1-3 by dielectric isolation walls. Either arrangement is useful.

FIG. 4 shows simplified flow chart 200 of a method of manufacture of thetransistors of FIGS. 1-3, according to further embodiments of thepresent invention. Method 200 begins with START 201 and initial step 202wherein a semiconductor containing substrate (e.g., SC 33) is providedhaving a first surface (e.g., surface 31). In step 204, a bipolartransistor (e.g., transistor 21, 51, 61) is formed in the substrate(e.g., SC 33) having: (i) a base (e.g., base 26 and/or 28) of a firstconductivity type and first dopant density; (ii) an emitter (e.g.,emitter 30) of a second, opposite, conductivity type and second dopantdensity; (iii) a collector (e.g., collector 24, 35) of the secondconductivity type and third dopant density; and (iv) wherein a portion(e.g., portion 28) of the base (e.g., base 26, 28), a base contact(e.g., base contact 32) and the emitter (e.g., emitter 30) extend to thefirst surface (e.g., surface 31). Method 200 has several alternateembodiments illustrated, for example, by implementations (a), (b), (c),(d) or (e). Implementation (a) comprises steps 202 and 204, path 205-1to step 206 and path 207 to END 214. In step 206, there is formed in theportion of the base at the first surface (e.g., portion 28) a furtherregion (e.g., region 48) of the second conductivity type and a fourthdopant density, extending laterally between the base contact (e.g.,contact 32) and the emitter (e.g., emitter 30). Implementation (b)comprises steps 202 and 204, path 205-2 to step 208 and path 209-1 toEND 214. In step 208, there is formed in the portion of the base (e.g.,portion 28) at the first surface (e.g., surface 31) a further region(e.g., region 48) of the second conductivity type and a fourth dopantdensity more than the first dopant density and less than the seconddopant density, extending laterally between the base contact (e.g.,contact 32) and the emitter (e.g., emitter 30). Implementation (c)comprises steps 202 and 204, path 205-2 to step 208, path 209-2 to step210 and path 211 to END 214. In step 210 there is formed in the portionof the base (e.g., portion 28) at the first surface (e.g., surface 31)between the further region (e.g., region 48) and the emitter (e.g.,emitter 30) a still further region (e.g., region 52) of the secondconductivity type and a fifth dopant density more than the fourth dopantdensity and less than the second dopant density. Implementation (d)comprises steps 202 and 204, path 205-2 to step 208, path 209-1 to step212 and path 213 to END 214. In step 212 there is formed laterally inthe emitter (e.g., emitter 30) proximate the first surface (e.g.,surface 31) a yet further region (e.g., region 62) of the secondconductivity type and a sixth dopant density, thereby deepening theemitter-base junction (e.g., junction 64) beneath the yet further region(e.g., region 62). Implementation (e) comprises steps 202 and 204, path205-1 to step 206 already described, path 207 to step 212 alreadydescribed and then path 213 to END 214. Implementations (a)-(e) and theparticular steps recited therein illustrate various steps included insuch implementations of method 200 and are not intended to implyparticular orders or sequences of such steps. All of the embodimentsillustrated by implementations (a)-(e) are useful. The embodiment(s)illustrated by implementation(s) (b) and (c) are preferred.

FIGS. 5-12 show simplified cross-sectional views of structures 504-511of bipolar transistors 21, 51, 61 of FIGS. 1-3 during various stages404-411 of manufacture. For convenience of explanation, the samereference numbers are used in FIGS. 5-12 as have been used in FIGS. 1-3to identify the various regions being formed during manufacturing stages404-411. The doping densities and/or concentrations described inconnection with FIGS. 1-3 apply to FIGS. 5-12 and such information isincorporated herein by reference. Ion implantation is a preferred dopingmeans, but any other doping means may also be used. Unless otherwisenoted, photoresist is a suitable masking material for such implants, butother masking materials may also be used. Referring now to manufacturingstage 404 of FIG. 5, SC 33 is provided comprising substrate 22 in or onwhich has been formed buried layer 24 and doped region 26′. In apreferred embodiment, BL 24 is formed in substrate 22 and then dopedregion 26′ extending to surface 31 is formed there-over by epitaxial(EPI) growth. However, other techniques may also be used to form BL 24and doped region 26′ in other embodiments. EPI region 26′ has thickness261′ usefully in the range of about 0.5 to 10 micrometers, moreconveniently about 0.75 to 5 micrometers and preferably about 1 to 3micrometers. The doping of base region 26 of FIGS. 1-3 is determined bythe doping of epi-region 26′ of FIG. 5, the prime (′) being used here toindicate that such region initially extends to surface 31. Whileepitaxial growth is a convenient means of forming doped region 26′ (andhence base region 26 of FIGS. 1-3) other fabrication means may be usedin other embodiments. Structure 504 comprising SC 33 results. Referringnow to manufacturing stage 405 of FIG. 6, shallow spaced-apart trenchisolation (STI) regions 361, 362 (collectively 36) of, for exampleinsulating material such as silicon oxide, are formed extending into SC33 from surface 31 in a conventional manner. Structure 505 results.

Referring now to manufacturing stage 406 of FIG. 7, mask 700 is appliedover surface 31 of structure 505. Mask 700 has openings 701, 702 inlocation and size appropriate for defining deep (e.g., N type) WELLs 35.Implant 703 is provided through openings 701, 702, thereby forming deepWELLs 35. A chain implant (e.g., N type) having energies, for exampleand not intended to be limiting, in the range of about 100-1000 KeV ispreferred, but other energies and other means for forming deep WELLs 35adapted to couple BL 24 to surface 31 in the indicated locations mayalso be used. Structure 506 results. Referring now to manufacturingstage 407 of FIG. 8, mask 700 used in manufacturing stage 406 isdesirably removed and mask 710 is applied over surface 31. Mask 710 hasopening 711 therein of size and location appropriate to form base region28 (e.g., P type) within EPI-layer 26′ of structure 506 between STIregions 362 and WELLs 35. Implant 712 (e.g., P type) is provided throughopening 711 to dope base region 28 as described in connection with FIGS.1-3. A chain implant having energies, for example and not intended to belimiting, in the range of about 20-200 KeV is preferred, but any othermeans of providing the desired doping may also be used. Structure 507results.

Referring now to manufacturing stage 408 of FIG. 9, mask 710 used inmanufacturing stage 407 is desirably removed and replaced by mask 720having opening 721 of width 723 and location appropriate for formingfurther doped regions 48 of FIGS. 1-3. Width 723 is preferably such asto span between about the centers of subsequently formed base contactregions 32 (e.g., see FIGS. 1-3 and 12), but smaller or larger widthsmay also be used in other embodiments. Implant 724 (e.g., N type) isprovided through opening 721 to form (e.g., N type) further region 48′.The convention is adopted of identifying the (e.g., N type) furtherregion formed in manufacturing stage 408 by reference number 48′including the prime, and then identifying those portions of region 48′that lie between subsequently formed emitter 30 and base contactregion(s) 32 (or between base contact region(s) 32 and still furtherregion(s) 52) by reference number 48 with the prime omitted (e.g., seeFIGS. 1-3). Structure 508 results. In still other embodiments a singleopening 721 may span the distance between, for example, about thecenters of STI regions 362, or multiple openings 721 may be providedcorresponding just to the desired locations of subsequent furtherregions 48 between emitter 30 (or still further region(s) 52) and basecontact region(s) 32. Either arrangement is useful. For convenience ofexplanation, it is presumed in manufacturing stages 409-411 of FIGS.10-12, that transistor 51 of FIG. 2 including regions 52 is beingformed. Persons of skill in the art will understand that transistor 21of FIG. 1 may be formed by omitting manufacturing stage 409. Themodifications of stage 409 needed to form transistor 61 of FIG. 3 arediscussed later. Referring now to manufacturing stage 409 of FIG. 10,mask 720 used in manufacturing stage 408 is removed and replaced withmask 730 having opening 731 of width 732. Implant 733 is providedthrough opening 731 to form doped region 52′ (e.g., N type), whichincludes regions 52 of FIG. 2 and, in this example, the subsequentlocation of emitter 30 between regions 52 (e.g., see FIG. 2). Again theconvention is followed of including a prime (e.g., as in 52′) toidentify the initial doped region, and omitting the prime from thoseportions (e.g., portions 52) of such initial region (e.g., region 52′)as remain after further doping steps. In other embodiments, implant 733may be omitted or be limited in area to just regions 52 of FIG. 2 ifdesired. Structure 509 results.

Referring now to manufacturing stage 410 of FIG. 11, mask 730 ofmanufacturing stage 409 is desirably removed. In a preferred embodiment,blocking layer 38 having portions 381, 382 of, for example an oxide andnitride stack, is applied and patterned as indicated, but may be omittedin other embodiments. Blocking layer 38 is useful, for example, indefining the lateral width of emitter 30 and in making separatedsilicided contacts to emitter 30 and base contact regions 32 and isincluded in a preferred embodiment, but may be omitted in otherembodiments. Mask 740 is provided over surface 31, having openings 741,742 corresponding to the desired locations of (e.g., N+) collectorcontacts 34, and opening 743 corresponding to the desired location of(e.g., N+) emitter 30. Portions 382 of blocking layer 38 are spacedapart by distance 744 and serve to substantially define the lateralextent of emitter 30. In an analogous manner, the lateral spacing of STIregions 361 and 362 determine the lateral width of collector contactregions 34. Implant 745 (e.g., N type) is provided through openings741-743 to obtain the doping concentrations and depths described inconnection with FIGS. 1-3. A typical (e.g., N type) source-drain typeimplant is generally suitable. Structure 510 results. Referring now tomanufacturing stage 411 of FIG. 12, mask 740 of manufacturing stage 410is desirably removed and replaced with mask 750 having openings 751, 752of location corresponding to base contact(s) 32 of FIGS. 1-3. Lateralspacings 753 between blocking layer portions 381, 382 substantiallydetermine the lateral width and location of base contact regions 32formed through mask openings 751, 752. Implant 754 is provided throughopenings 751, 752 to form base contact(s) 32 as described in connectionwith FIGS. 1-3. A typical (e.g., P type) source-drain type implant isgenerally suitable. Structure 511 results. Passivation layers andconductive (e.g., silicided) contacts are then applied in a conventionalmanner to obtain the structures illustrated in FIGS. 1-3.

Referring again to manufacturing stages 409-410 of FIGS. 10-11, theconfiguration illustrated by transistor 61 of FIG. 3 is formed bychoosing width 732 of mask opening 731 of FIG. 10, used to locateimplant 733 for yet further region 62, to be smaller than width 744 ofthe gap between blocking layer portions 382 under mask opening 743 ofFIG. 11 used to locate (emitter) implant 745. In this manner, yetfurther region 62 can be formed laterally within emitter 30 (see FIG.3). In a preferred embodiment, implant 733 for forming region 62conveniently comprises a somewhat smaller dose than implant 745 forforming emitter 30 and energies that are approximately comparable to oroverlap those of implant 745 for forming emitter 30, but other doses andenergies can also be used. This combination of implants 733 and 745desirably provides emitter-base junction 64 (see FIG. 3) under region 62slightly below the depth of emitter-base junction 66 (see FIG. 3)beneath the remainder of emitter 30 laterally outside of further region62. Channeling of doping atoms during the implant is believed tosomewhat counter dope the part of base portion 28 underlying region 62thereby lowering the effective base doping concentration therein andincreasing the observed beta of transistor 61. This is desirable.

According to a first embodiment, there is provided a bipolar transistor(21, 511 61) having a first surface (31), and comprising a base (26, 28)of a first conductivity type having a first portion (28) extending inpart to the first surface (31), a collector (24, 35) of a second,opposite, conductivity type in contact with the base (26, 28), anemitter (30) of the second conductivity type extending into the base(26, 28) at the first surface (31), a base contact (32) of the firstconductivity type extending into the base (26, 28) at the first surfaceand laterally spaced apart from the emitter (30) at the first surface(31), and a further region (48) of the second conductivity type locatedlaterally between the emitter (30) and the base contact (32) proximatethe first surface (31). According to a further embodiment, the base (26,28) has an upper first region (28) and a lower second region (26),wherein the first region (28) of the base (26, 28) has a first dopantconcentration, the emitter (30) has a second dopant concentration, thebase contact (32) has a third dopant concentration, and the furtherregion (48) has a fourth dopant concentration, and wherein the fourthdopant concentration is intermediate between the first and second dopantconcentrations. According to a still further embodiment, the transistor(51) further comprises a still further region (52) of the secondconductivity type located proximate the first surface (31) laterallybetween the further region (48) and the emitter (30). According to a yetfurther embodiment, the still further region (52) has a fifth dopantconcentration intermediate between the second and fourth dopantconcentrations. According to a still yet further embodiment, the emitter(30) has a first lateral width (65) and the transistor (61) additionallycomprises a yet further region (62) of the second conductivity type anda second lateral width (63) smaller than the first lateral width (65).According to a yet still further embodiment, the emitter forms a firstemitter-base junction of a first depth (66) and the yet further region(62) forms a second emitter-base junction of a second depth (64) deeperthan the first depth (66). According to another embodiment, the firstregion (28) of the base (26, 28) has a first dopant concentration aboutin the range of 1E14 to 1E19 cm⁻³, the emitter (30) has a second dopantconcentration about in the range of 1E19 to 1E23 cm⁻³, the base contact(32) has a third carrier concentration about in the range of 1E19 to1E23 cm⁻³, and the further region (48) has a fourth carrierconcentration about in the range of 1E16 to 5E19 cm⁻³. According tostill another embodiment, the first region (28) of the base (26, 28) hasa first dopant concentration about in the range of 1E14 to 1E19 cm⁻³,the emitter (30) has a second dopant concentration about in the range of1E19 to 1E23 cm⁻³, the base contact (32) has a third carrierconcentration about in the range of 1E19 to 1E23 cm⁻³, the furtherregion (48) has a fourth carrier concentration about in the range of1E16 to 5E19 cm⁻³, and the still further region (52) has a dopantconcentration in the range of about 1E16 to 1E20 cm⁻³.

According to a second embodiment, there is provided a method (200) forforming an electronic device (21, 51, 61), comprising the steps of,providing a semiconductor containing substrate (33) having a firstsurface (31), forming a bipolar transistor by providing in the substrate(33), a base (26, 28) of a first conductivity type and a first dopantdensity, an emitter (30) of a second opposite conductivity type and asecond dopant density, and a collector (34, 35) of the secondconductivity type and a third dopant density, wherein a portion (28) ofthe base (26, 28), a base contact (32) and the emitter (30) extend tothe first surface (31), and forming in the portion (28) of the base (26,28) at the first surface (31) a further region (48) of the secondconductivity type and a fourth dopant density located laterally betweenthe base contact (32) and the emitter (30). According to a furtherembodiment, the fourth dopant density is more than the first dopantdensity and less than the second dopant density. According to a stillfurther embodiment, the method (200) further comprises forming in theportion (28) of the base (26, 28) at the first surface (31) a stillfurther region (52) of the second conductivity type and a fifth dopantdensity different than the fourth dopant density. According to a yetfurther embodiment, the still further region (52) is located laterallybetween the further region (48) and the emitter (30). According to astill yet further embodiment, the fifth dopant density is more than thefourth dopant density and less than the second dopant density. Accordingto a still yet further embodiment, the method (200) additionallycomprises forming a yet further region (62) of the second conductivitytype extending at least partly below the emitter (30). According to ayet still further embodiment, the yet further region (62) has anemitter-base junction (64) within the second region (28) deeper than anemitter-base junction formed by a portion of the emitter (30) lyinglaterally outside the yet further region (62).

According to a third embodiment, there is provided a semiconductordevice (21, 51, 61), comprising coupled NPN or PNP regions and contactsthereto (24, 35, 26, 28, 30, 32, 34) having portions (28, 30, 32, 34)extending to a first surface (31), wherein a first portion (28) of afirst conductivity type has an Ohmic contact region (32) therein of thefirst conductivity type at the first surface, a second portion (30) of asecond opposite conductivity type extends into the first portion (28) atthe first surface (31) forming an NP or PN junction (64) therewithlaterally spaced apart from the contact region (32) at the first surface(31), and a further region (48) of the second conductivity type in thefirst portion (28) forming an NP or PN junction therewith, wherein thefurther region (48) extends laterally substantially between the secondportion (30) and the contact region (32) at the first surface (31).According to a further embodiment, the first portion (28) has a firstdopant concentration, the second portion (30) has a second dopantconcentration, the contact region (32) has a third dopant concentration,and the further region (48) has a fourth dopant concentration greaterthan the first and less than the second dopant concentration. Accordingto a still further embodiment, the device additionally comprises a stillfurther region (52) of the second dopant type coupled between thefurther region (48) and the second portion (30) at the first surface(31). According to a yet further embodiment, the still further region(52) has a fifth dopant concentration intermediate between the fourthand second dopant concentrations. According to a still yet furtherembodiment, the second portion (30) has a first junction depth (66) withthe first portion (28), and wherein the device (61) additionallycomprises a yet further region (62) of the second conductivity typehaving a second junction (64) depth with the first portion (28) greaterthan the first junction depth (66).

While at least one exemplary embodiment and method of fabrication hasbeen presented in the foregoing detailed description of the invention,it should be appreciated that a vast number of variations exist. Itshould also be appreciated that the exemplary embodiment or exemplaryembodiments are only examples, and are not intended to limit the scope,applicability, or configuration of the invention in any way. Rather, theforegoing detailed description will provide those skilled in the artwith a convenient road map for implementing an exemplary embodiment ofthe invention, it being understood that various changes may be made inthe function and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims and their legal equivalents.

What is claimed is:
 1. A bipolar transistor having a first surface, andcomprising: a base of a first conductivity type; a collector of asecond, opposite, conductivity type in contact with the base; an emitterof the second conductivity type extending into the base at the firstsurface and having a first lateral width; a base contact of the firstconductivity type extending into the base at the first surface andlaterally spaced apart from the emitter; a further region of the secondconductivity type located laterally between the emitter and the basecontact and formed in the base proximate the first surface, the furtherregion extending from the base contact toward the emitter and having apeak dopant concentration near the first surface less than the dopingconcentration of the emitter; and a yet further region of the secondconductivity type and a second lateral width smaller than the firstlateral width.
 2. The transistor of claim 1, wherein the base has anupper first region and a lower second region, wherein the first regionof the base has a first dopant concentration, the emitter has a seconddopant concentration, the base contact has a third dopant concentration,and the further region has a fourth dopant concentration, and whereinthe fourth dopant concentration is intermediate between the first andsecond dopant concentrations.
 3. The transistor of claim 2, furthercomprising a still further region of the second conductivity typelocated proximate the first surface laterally between the further regionand the emitter.
 4. The transistor of claim 3, wherein the still furtherregion has a fifth dopant concentration intermediate between the secondand fourth dopant concentrations.
 5. The transistor of claim 2, whereinthe first region of the base has a first dopant concentration about inthe range of 1E14 to 1E19 cm⁻³, the emitter has a second dopantconcentration about in the range of 1E19 to 1E23 cm⁻³, the base contacthas a third carrier concentration about in the range of 1E19 to 1E23cm⁻³, and the further region has a fourth carrier concentration about inthe range of 1E16 to 5E19 cm⁻³.
 6. The transistor of claim 3, whereinthe first region of the base has a first dopant concentration about inthe range of 1E14 to 1E19 cm⁻³, the emitter has a second dopantconcentration about in the range of 1E19 to 1E23 cm⁻³, the base contacthas a third carrier concentration about in the range of 1E19 to 1 E23cm⁻³, the further region has a fourth carrier concentration about in therange of 1E16 to 5E19 cm⁻³, and the still further region has a dopantconcentration in the range of about 1E16 to 1E20 cm⁻³.
 7. The transistorof claim 1, wherein the emitter forms a first emitter-base junction of afirst depth and the yet further region forms a second emitter-basejunction of a second depth deeper than the first depth.
 8. A bipolartransistor having a first surface, comprising: a base of a firstconductivity type; a collector of a second, opposite conductivity typein contact with the base; an emitter of the second conductivity typeextending into the base at the first surface; a base contact of thefirst conductivity type extending into the base at the first surface andlaterally spaced apart from the emitter; and at least one near-surfaceregion of the second conductivity type formed in the base immediatelyunder the first surface and extending laterally from the emitter to thebase contact, the at least one near-surface region comprising an area ofthe base having a modified doping reducing the surface effects in thebase between the emitter and the base contact to improve the stabilityof the bipolar transistor; wherein the at least one near-surface regioncomprises a further region extending from the base contact toward theemitter, wherein the further region has a peak doping concentration lessthan the peak doping concentration of the emitter, and wherein thedoping profile of the further region falls to about equal to or lessthan that of the base region within a depth below the first surface lessthan the emitter depth.
 9. The bipolar transistor of claim 8 wherein thefurther region has a surface concentration about an or order of amagnitude larger than the doping density of the base region.
 10. Thebipolar transistor of claim 8 wherein the further region contacts boththe base contact and the emitter.
 11. The bipolar transistor of claim 8further comprising a blocking layer overlying the first surface andcovering the at least one near-surface region, the blocking layer havingopenings therein through which the emitter and base contact are exposed.12. The bipolar transistor of claim 8 further comprising a yet furtherregion formed immediately under the emitter and in contact therewith,the yet further region moving an emitter-base junction of the bipolartransistor deeper into the base relative to the first surface.
 13. Abipolar transistor having a first surface, comprising: a base of a firstconductivity type; a collector of a second, opposite conductivity typein contact with the base; an emitter of the second conductivity typeextending into the base at the first surface; a base contact of thefirst conductivity type extending into the base at the first surface andlaterally spaced apart from the emitter; and at least one near-surfaceregion of the second conductivity type formed in the base immediatelyunder the first surface and extending laterally from the emitter to thebase contact, the at least one near-surface region comprising an area ofthe base having a modified doping reducing the surface effects in thebase between the emitter and the base contact to improve the stabilityof the bipolar transistor, the at least one near-surface regioncomprising: a further region extending from the base contact toward theemitter, the further region having a peak doping concentration less thanthe peak doping concentration of the emitter; and a still further regionextending from the further region to the emitter, the still furtherregion having a doping concentration greater than that of the furtherregion.
 14. The bipolar transistor of claim 13 wherein the furtherregion has a surface concentration about an or order of a magnitudelarger than the doping density of the base region.
 15. The bipolartransistor of claim 13 wherein the further region contacts both the basecontact and the emitter.
 16. The bipolar transistor of claim 13 furthercomprising a blocking layer overlying the first surface and covering theat least one near-surface region, the blocking layer having openingstherein through which the emitter and base contact are exposed.
 17. Thebipolar transistor of claim 13 further comprising a yet further regionformed immediately under the emitter and in contact therewith, the yetfurther region moving an emitter-base junction of the bipolar transistordeeper into the base relative to the first surface.